Wires of the world … racks of servers are vital infrastructure in a digital economy. Photograph: Martial Trezzini/EPA

In a world where increasing amounts of our data are held somewhere in vast server farms, the opening of a new data centre in Wiltshire may seem like no big thing. Enormous sheds filled with racks of computers pop up every day and everywhere, the silent power strengthening the ever-more-connected and ever-more-digital world.

But in Ark Continuity's new SQ17 server farm buried deep in the former stone mines of Corsham, is something worth noting. The facility, unveiled today, is probably the most sustainable and environmentally friendly of its kind in the world: a combination of location and design means that it uses more than a third less energy than a typical data centre.

"Between 25-40% of the cost of running a data centre would be in the electricity," says Jeffrey Thomas, chief executive of Ark Continuity. "So if we can cut that in half, we're making a significant economic saving for our occupiers, even before their CO2 reduction obligations."

IT accounts for around 2% of the UK's carbon emissions and the sector is aware of increasing impact it will have on energy and environment as it grows. "Being more efficient in the data centre is synonymous not only with saving carbon but also saving money," says Kate Craig-Wood, co-founder of the carbon-neutral ISP Memset. "So it's pretty common sense really."

Digital Europe, the EU-wide trade body for the tech sector, has committed to getting its members to reduce their emissions by 20% by 2020, relative to 2008 levels. Given that the number of servers is expected to increase globally from 13m in 2008 to 122m by 2020, the potential energy footprint is a serious issue.

"We are passionate about the future of this planet," says Thomas. "It is the only and right way to do things."

He acquired what is now known as Spring Park ten years ago. A hundred miles from London and with a million-square-feet hole underground, it was not immediately obvious to Thomas that the site should be used as a data centre. The facility had been an underground munitions dump and factory site during the Second World War. "In the Cold War, latterly under Macmillan and Thatcher, it became the seat of government in a time of crisis. Part of it became a nuclear bunker."

This meant the underground buildings were some of the most secure facilities in the UK, reinforced and strengthened so that they could withstand three 10-megaton nuclear strikes at the same time. And it also had interesting environmental characteristics – being a damp mine, it was ideal at staying cool. "The sun never shines down there so there's no solar gain," says Thomas. "With the size of it and the evaporative qualities of the mine, we can dissipate 20MW of energy with adiabatic cooling with 10 litres of water a second, which is just cycled around in a fog underground."

"At our latitude and altitude, we'll get around 60-65% of the year we should achieve free air cooling – that means the temperature of the outside of the building is cool enough to use to cool the inside of the building."

The server space at Spring Park costs around 20% more to build than typical setups, thanks to the cleaner technologies involved. Rather than using cooling systems with greenhouse gas refrigerants, SQ17 uses chilled water. "And that costs more but is lower carbon – some of the technologies cost more, the design is more sophisticated." But this leads to much lower operational costs, mainly in electricity savings.

The efficiency of a data centre can be assessed using the power usage effectiveness (PUE), a measure of the amount of power needed for cooling and other management (such as lights and security) for every kilowatt consumed by the IT infrastructure. The UK average is around 2.2: for every kilowatt spent on IT, 1.2 KW used to cool and manage the space. "Best practice PUE around 1.5 and there are some stellar examples where you might get to 1.2 or 1.3 but they're typically not the most robust data centres," says Thomas.

At Spring Park, for those days where the surface temperature is above 18C, Thomas says the ground source cooling mechanism does all the required work and the PUE of the data centre gets down to between 1.09 and 1.12.

Other factors that raise the energy costs of data centres include redundancy and security. Doubling up hardware in case anything failed was the obvious thing to do when servers were not as efficient or reliable, says Craig-Wood. But nowadays it just wastes resources and it is possible to be smarter about how ISPs and data centre operators manage failures. The EU's new code of conduct for data centres even recommends that consumers shy away from doubling up and only use what they need. Craig-Wood says that, in most cases, doubling the number of servers is simply not necessary.

Another reason Spring Park uses less energy is location. "Before 9/11," according to Thomas, "every data centre had to be based in London for the UK and everyone wanted to hug their servers."

With improvements in technology infrastructure and broadband connections, it began to matter less where data was physically located, so the biggest driver became sustainability. "London is 1.5-2C warmer than Wiltshire – so we enjoy an 18% addition free air cooling by just not being in London."

Craig-Wood, who also sits on the energy and environment working group of Intellect, the UK's high-tech trade body, said that in addition to meeting its own commitments, IT will play important roles in helping other sectors reduce their carbon impact in the coming years. Through smart logistics, smart buildings and tele-working, she says that intelligent applications of IT could help Europe cut around 15% of its CO2 emisssions by 2020. "High-tech capacity and IT has the capacity to be one of the new engines of growth to bring us out of the recession," she says. "So it's important we do it but in a sustainable way."